Plants encounter a variety of environmental stresses that effect plant water status. The availability of water for nutrient transport, cellular metabolism, evaporative cooling and other biological functions is often impaired by these environmental stresses. One mechanism that all organisms use to tolerate abiotic stress is the accumulation of solutes that do not interfere with normal biochemical reactions. Three of the most effective compatible solutes, as shown by in vitro enzyme stabilization studies are ectoine, hydroxyectoine (unusual methylated cyclic amino acids) and trehalose (Lippert, K. et al. (1992) Appl. Microbiol. Biotech. 37:61-65). In fungi, bacteria and invertebrates trehalose plays a major role in desiccation tolerance and several genes have been identified in bacteria that encode enzymes required for trehalose biosynthesis (Bohnert, H. J. et al. (1995) Plant Cell 7:1099-1111). Two of the enzymes involved in trehalose biosynthesis are alpha, alpha-trehalose-phosphate synthase, and trehalose-6-phosphate phosphatase. Trehalose is metabolized by the enzyme alpha, alpha-trehalase. Initially, plants were thought to lack the ability to synthesize trehalose and attempts have been made to engineer water-stress tolerance in plants via the expression of microbial genes for trehalose synthesis. However, it has been demonstrated that Arabidopsis thaliana possesses a gene for trehalose-6-phosphate synthase, TPS1 (Blazquez et al. (1998) Plant J 13:685-689) and at least two genes, AtTPPA and AtTPPB, for trehalose-6-phosphate phosphatase (Vogel, G. et al. (1998) Plant J 13(5):673-683). Thus there is a great deal of interest in identifying genes that encode proteins that may be involved in trehalose synthesis in plants. These genes may be used to engineer trehalose synthesis in plants in an effort to produce plants with increased water stress tolerance. Accordingly, the availability of nucleic acid sequences encoding all or a portion of a trehalose-6-phosphate phosphatase, alpha, alpha-trehalase and alpha, alpha-trehalose-phosphate synthase would facilitate studies to better understand or engineer trehalose synthesis in plants and provide genetic tools to produce plants having increased water stress tolerance.